1. Field of the Invention
The present invention relates to a pneumatic spring hammer device.
Pneumatic spring hammer devices are standardly used in drilling and/or striking hammers (called “hammers” in the following) in order to exert impacts on a tool at regular intervals. For this purpose, a design has proven successful in which a drive sets a drive piston into an axial back-and-forth motion that is transmitted to an impact piston via an air spring that arises in a hollow space between the drive piston and the impact piston. Finally, the impact piston strikes the tool or a header situated between the piston and the tool.
In a preferred design for such a pneumatic hammer device, the drive piston is fashioned so as to be hollow on its front side, the impact piston being guided in the cavity of the drive piston. This is also referred to as a hollow piston hammer device.
This design has proven to be very successful in practice; due to the low mass of the drive piston only slight idle oscillations occur, and no seal is required between the pistons. However, a disadvantage is that the transition between idle operation and impact operation does not always take place with the desired degree of precision, resulting in a higher risk of idle hammering when the operator actually desires to change over to idle operation. Impacts with lower intensity, or even undesired idle operation, can also result if the operator does not press the hammer fully against the material to be processed, or if the impact piston recoil does not take place. In both cases, operability and/or work results are adversely affected.
2. Description of the Related Art
From U.S. Pat. No. 6,523,622 B1, a hollow piston hammer device having a return spring is known. Here a control disk is provided that interrupts a connection to the return spring when there is a changeover between impact operation and idle operation, while an idle opening is moved over an air duct, so that a hollow space that accommodates the air spring can be brought into connection with the surrounding environment.
In DE 198 47 687 A1, a hollow piston hammer device having sleeve controlling is described. The sleeve controlling enables a reliable and precise changeover between idle operation and impact operation, using a control sleeve that can be axially displaced. When the control sleeve is in the idle position, the hollow space formed between the drive position and the impact piston.
The hollow piston hammer device according to DE 198 47 687 A1 has performed outstandingly in practice. Nonetheless, it has been noted that improvements could be made with respect to its strength and sealing properties.